SPECIFIC AIMS 1. To define and map specific chronic pain synromes after SCI using psychophysical testing of somatosensory pathways. 2. To determine analgesic efficacy of dextromethorphan (by NMDA receptor blockade) in spontaneous and evoked pain after SCI. 3. To determine analgesic efficacy of gabapentin (by potentiation of GABA release) in spontaneous and evoked pain after SCI. 4. To determine whether analgesia is augmented when therapy is aimed at two potential pain mechanisms, blockade of excitatory pathways and enhancement of descending inhibitory pathways. PSYCHOPHYSICAL TESTING: Detailed sensory testing and psychophysics provide a quantitative method of pain measurement to aid in the understanding of neural mechanisms in pain. In this study, the investigators are delivering: 1) warm and cool stimuli to the skin to assess Ad and C fiber function; 2) low frequency mechanical stimuli to stimulate a subset of Ab fibers; and 3) transcutaneous constant current electrical stimuli to provide low amplitude current through the skin to assess Ab and A8 fiber function. Psychophysical testing of somatosensory functions allows the investigators to 1) assess the precise characteristics of the pain, 2) evaluate differential treatment responses to dextromethorphan or gabapentin, and 3) monitor changes in somatosensory function over time. Differences in treatment responses between patients with different pain syndromes after SCI will provide new insights regarding pathways through which these various pain states are medicated.